•VUV spectroscopic properties of rare-earth ions in Ba6Gd9B79O138 have been investigated.•The CT bands of O2--Sm3+ and O2--Eu3+ charge transfer bands were observed at 202 and 249 nm, respectively.•The f-d spin-allowed (208 nm) and spin-forbidden (230 nm) transitions of Tb3+ were observed.•Energy transfer from the host to rare-earth activators has been demonstrated.Vacuum ultraviolet (VUV) spectroscopic properties of rare-earth RE3+- activated (RE3+ = Sm3+, Eu3+, Tb3+ and Dy3+) Ba6Gd9B79O138 borates (BGBO) are investigated. The strong absorption bands in the VUV range of un-doped and RE3+-activated BGBO were observed. The band range from 140 to 200 nm with a peak at about 173 nm results from the host lattice absorption. For Sm3+-activated BGBO, the charge transfer transition from O2- to Sm3+ was observed at 202 nm. In addition, it exhibits bright red emission originating from the Sm3+f-f transitions of 4G5/2 → 6HJ (J = 5/2, 7/2 and 9/2). The O2--Eu3+ charge transfer (CT) at 249 nm is observed in the excitation spectrum for Eu3+-doped BGBO. For Tb3+-activated BGBO, the broad bands around 208 and 230 nm are due to the spin-allowed and spin-forbidden f-d transitions of Tb3+, respectively. In addition, the absence of the f-d transitions of Sm3+ and Dy3+ in the excitation spectra probably due to the photo-ionization effect. It is demonstrated that there are energy transfers from the BGBO host lattice to the luminescent activators depending on the activators.

This work reports self-assembled uniform monodisperse NaxY(OH)yF3+x–y (0 < x < 1, 0 < y < 3) mesocrystals with tunable morphology and chemical composition obtained from a hydrothermal ion-exchange reaction. Detailed crystal structure analysis illustrates that the special crystal structure of NaxY(OH)yF3+x–y (0 < x < 1, 0 < y < 3) facilitates the pH-mediated ion-exchange process. A possible topochemical-based mechanism has been proposed to this ion-exchange process. By carefully adjusting the pH value of the solution, the tunable three-dimensional (3D) NaxY(OH)yF3+x–y (0 < x < 1, 0 < y < 3) mesocrystal architectures are obtained through an oriented self-assembly. The photoluminescence properties of the rare earth ions (such as Eu3+, Tb3+, and Ce3+) doped as-prepared mesocrystal samples are investigated, and multicolor emissions are realized.

This communication reports the synthesis of CC functionalized oleophilic carbon dots (FOCDs). The as-prepared FOCDs could enhance the stability of optical polymer against UV aging while no obvious effect on optical transparency.

•An alternate spin-coating method was firstly carried out for Lu2O3: Eu3 + film fabrication.•The denser and thicker Lu2O3: Eu3 + polycrystalline film was achieved by the optimized spin-coating method.•The emission intensity of the film fabricated by the optimized technique enhances as much as 72%.•Emission spectral features of Lu2O3: Eu3 + associated with Eu3 + sites occupancy was illustrated via VASP calculation and crystallographic analysis.Europium-doped Lutetium oxide (Lu2O3: Eu3 +) polycrystalline films have been successfully fabricated on cleaned silicon (100) substrates by routine and alternate spin-coating techniques. X-ray diffraction (XRD), photoluminescence (PL) spectra, field emission electron scanning microscope (FE-SEM) are employed to characterize the as-fabricated films. The SEM observation reveals that the thickness and porosity of the film fabricated by the alternate spin-coating are superior to that by routine spin-coating, i.e. the thickness and porosity increase 95% and reduce 26%, respectively, resulting in 72% enhancement of the emission intensity. According to theoretical calculation and crystallographic analysis, the dominated 5D0-7F2 emission of Eu3 + can be assigned to the main non-inversion site occupancy.

•Typical 5d–4f transition of Ce3+ and defect-related luminescence of the host have been observed in Ce3+ doped sample.•The small band gap and weak absorption in the VUV range of the host lattice have been clarified.•The Ce3+ ion was demonstrated to occupy Sr3 site (6g, C1) in the host.•The XEL and VUV–UV luminescence mechanisms have been investigated in detail.The apatite related compound Sr10[(PO4)5.5(BO4)0.5]BO2 (SrBPO) doped with Ce3+ was synthesized via solid state reaction method. Undoped SrBPO shows blue-green emission under ultraviolet (UV) and X-ray excitation due to the defects in the host. When excited by vacuum ultraviolet–ultraviolet (VUV–UV) light or X-ray, Ce3+ doped SrBPO shows a broad emission band peaking at 450 nm originating from 5d–4f transition of Ce3+ and defects in the host. The phosphor exhibits strong excitation bands in UV range and a weak broad excitation band in VUV region. The site occupation of Ce3+ was proposed based on fluorescence decay curves. Electronic structure shows the compound is an indirect semiconductor with a band gap of 3.04 eV. The extremely small density of states of [PO4]3− or [BO4]5− group near Fermi level or in the conduction band is a possible origin of the weak excitation band in the VUV range. A possible mechanism was proposed to explain the luminescence properties observed.

RE3+ (RE = Pr, Sm, and Tb)-doped SrAlSi4N7 samples were synthesized by a solid-state reaction method at high temperature, and their photoluminescence properties were investigated. It is noticeable that the 5d bands of Pr3+ and Tb3+ are at rather low energy in SrAlSi4N7 compared to oxides. Typical 4f2 → 4f2 emission lines (480–800 nm) of Pr3+ under 4f2 → 4f15d1 excitation were observed in Pr3+-doped SrAlSi4N7. Sm3+-doped SrAlSi4N7 shows red emission originating from 4G5/2 → 6HJ (J = 5/2, 7/2 and 9/2) transitions, and the charge transfer band of Sm3+ was observed at an unusually low energy of 3.98 eV. The Tb3+-doped sample exhibits 5D3 → 7FJ (J = 6, 5, 4, 3, 2, 1) (blue) and 5D4 → 7FJ (J = 6, 5, 4, 3) (green) line emissions in the wavelength range of 375–650 nm under the direct Tb3+ 4f8 → 4f75d1 excitation. The bands at about 256 nm in the excitation spectra are attributed to the host lattice absorption. In addition, there is energy transfer from the host lattice to the luminescent activators (Pr3+, Sm3+, and Tb3+). The energy level diagram containing the position of the 4f and 5d levels of all divalent and trivalent lanthanide ions relative to the valence and conduction band of SrAlSi4N7 has been constructed and discussed.

Monodispersed yttrium aluminum garnet (YAG) crystallites with well-developed and controllable crystal faces were obtained by the solvothermal method. The effects of temperature, time, and solvents on the phase formation, morphology, and particle size distribution were investigated. YAG can be obtained at relatively lower temperature in water, while higher temperature and longer time are necessary with increasing amount of ethanol in the solvent. The presence of {100} faces is favored at lower temperature while the terminating faces are {110} and {211} at higher temperature in water and water–ethanol mixture (volume ratio = 1:1). Moreover, solvent exhibits a significant influence on the reaction process, luminescence intensity, and decay time of YAG:Ce crystallites. This study presents a novel way to obtain YAG crystallites with well-developed terminating faces which will be promising in the solid-state lighting and will lay a foundation to study the grain boundaries formed in the process of YAG transparent ceramics sintering.

•The site occupation of rare-earth ions in Y4Si2O7N2 has been determined using first principle method.•The 5d-4f and 4f-4f emissions, instead of the cascade emission of Pr3+ were observed.•The CT band of Sm3+ was observed at a relatively lower energy of 4.68 eV.•The cross-relaxation of the emission between Tb3+ ions in Y4Si2O7N2 was demonstrated.•A detailed energy level diagram of Y4Si2O7N2 has been constructed and discussed.RE3+ (RE = Pr, Sm, Tb, Er, Dy)-activated Y4Si2O7N2 samples were prepared by a solid-state reaction method at high temperature, and their photoluminescence properties were investigated. The absorption band located at about 250 nm is attributed to the host absorption. The 5d bands of Pr3+ and Tb3+ are at rather low energy in Y4Si2O7N2 compared to oxide. The direct Pr3+ 4f2 → 4f15d1 excitation at 275 nm leads to typical 4f2 → 4f2 line emissions (450–700 nm) and strong 4f15d1 → 4f2 broad band emission (300–450 nm), respectively. The charge transfer (N3− → Sm3+) band of Sm3+ was observed at a somewhat lower energy of 4.68 eV compared to oxide, and Sm3+-activated sample shows a bright red emission originating from 4G5/2 → 6HJ (J = 5/2, 7/2 and 9/2) transitions. For Tb3+-doped sample, the direct Tb3+ 4f8 → 4f75d1 excitation leads to 5D3 → 7FJ (J = 6, 5, 4, 3) (blue) and 5D4 → 7FJ (J = 6, 5, 4, 3) (green) line emissions, the cross-relaxation depended on Tb concentration has happened. The incorporation of Er3+ (or Dy3+) into Y4Si2O7N2 resulted in a typical Er3+ (or Dy3+) f-f line absorptions and emissions. Moreover, the energy transfer from the host lattice to the luminescent activators (Pr3+, Tb3+ and Sm3+) is observed. The energy level diagram containing the position of 4f and 5d energy levels of all Ln2+ and Ln3+ ions relative to the valence and conduction band of Y4Si2O7N2 has been established and studied based on the data presented in this work, and further provides a platform for studying the photoluminescence properties as well as the valence stability of the lanthanide ions.Energy level scheme showing the 4f ground states of the trivalent (filled square) and divalent ions (filled circle) and lowest energy 5d states of the trivalent (open square) and divalent ions (open circle) relative to the valence and conduction band of Y4Si2O7N2. The red dashed horizontal line is the optical band gap of Y4Si2O7N2. The arrows (1–4) indicate the experimentally determined transitions used to construct this scheme.

•RE3+-doped Ln7O6F9 nano-rods were obtained without extra fluorine source through a facile hydrothermal method.•The tip of the nano-rods exhibits varying degrees of bifurcation phenomena.•The charge transfer band (CTB) and f → d transition were observed in Eu3+ and Pr3+-doped Ln7O6F9, respectively.The uniform 1D nano-rods of RE3+ doped Ln7O6F9 (Ln = Y and Lu; RE = Pr, Sm and Eu) were synthesized through a facile two-step hydrothermal method without extra fluorine source followed by post-heat treatment. The phase formation, morphologies, as well as photoluminescence properties of the materials were investigated. The precursor composition was determined to be Ln(OH)1.69F1.31 using the Fourier transform infrared spectrum (FT-IR), thermal gravimetric and differential scanning calorimetry (TG-DSC). The average lengths of Y7O6F9 and Lu7O6F9 were about 6.8 and 7.9 μm, respectively, with the average width of about 650 nm. It was interesting that the tip of the nano-rods exhibits a straight line and divergent umbrella shaped bifurcation for Y7O6F9 and Lu7O6F9, respectively. Upon ultraviolet excitation, Pr3+, Sm3+ and Eu3+ ions in Ln7O6F9 showed blue, orange and red emissions originating from their characteristic f-f transitions. In addition, the 4f15d1 → 4f2 band emissions (340–450 nm) as well as typical 4f2 → 4f2 line emissions (450–700 nm) of Pr3+ were observed in Pr3+-doped Ln7O6F9. For Sm3+-doped Ln7O6F9, only the typical f - f transitions of Sm3+ were observed with the absence of charge transfer (CT) band. However, the broad excitation bands at 255 nm attributing to the charge transfer transition of Eu3+ (i.e. O2− → Eu3+ CT) were observed in Eu3+-doped Ln7O6F9.

RE3+ (RE = Pr, Sm, and Tb)-doped SrAlSi4N7 samples were synthesized by a solid-state reaction method at high temperature, and their photoluminescence properties were investigated. It is noticeable that the 5d bands of Pr3+ and Tb3+ are at rather low energy in SrAlSi4N7 compared to oxides. Typical 4f2 → 4f2 emission lines (480–800 nm) of Pr3+ under 4f2 → 4f15d1 excitation were observed in Pr3+-doped SrAlSi4N7. Sm3+-doped SrAlSi4N7 shows red emission originating from 4G5/2 → 6HJ (J = 5/2, 7/2 and 9/2) transitions, and the charge transfer band of Sm3+ was observed at an unusually low energy of 3.98 eV. The Tb3+-doped sample exhibits 5D3 → 7FJ (J = 6, 5, 4, 3, 2, 1) (blue) and 5D4 → 7FJ (J = 6, 5, 4, 3) (green) line emissions in the wavelength range of 375–650 nm under the direct Tb3+ 4f8 → 4f75d1 excitation. The bands at about 256 nm in the excitation spectra are attributed to the host lattice absorption. In addition, there is energy transfer from the host lattice to the luminescent activators (Pr3+, Sm3+, and Tb3+). The energy level diagram containing the position of the 4f and 5d levels of all divalent and trivalent lanthanide ions relative to the valence and conduction band of SrAlSi4N7 has been constructed and discussed.